(1). Field of the Invention
The present invention relates to a cassette for loading glasses for liquid crystal displays and a method for discharging electrostatic charges generated in glasses.
(2). Description of the Prior Art
Nowadays, a liquid crystal display is widely used due to its properties of slim thickness, light weight and low power consumption. In manufacturing the liquid crystal display, a glass is used as a back-frame of the device and the step of transferring the glass is necessary. When the glasses are transferred to another place, they are loaded on cassettes and the cassettes are carried by men or machines.
Hereinafter, the cassette for loading and carrying the glasses will be explained with reference to the attached drawings.
FIG. 1 is a perspective view of a conventional cassette for loading the glasses, and FIGS. 2 and 3 are a front and a side view of the conventional cassette shown in FIG. 1, respectively.
As shown in FIGS. 1 to 3, the conventional cassette 10 for loading the glasses comprises side plates 11 having slots 15 formed of protrusions 15' for loading the glasses therein, a bottom board 12 and a top board 13. The cassette 10 further includes stoppers 14 for preventing the drifting away of the glasses from the cassette 10 when carrying the glasses in the cassette 10, and handles 16 for convenient carrying the cassette 10. In operation, a user loads the glasses on the cassette 10 by inserting the glasses in the slots 15 of the side plates 11. After loading the glasses on the cassette 10, the user carries the cassette 10 with maintaining the front side of the cassette 10 to be a little up in order to preventing the sliding away of the glasses from the cassette via the front side of the cassette 10. It is because the conventional cassette 10 has no element for blocking the sliding away of the glasses via the front side of the cassette 10. Accordingly, if the cassette 10 leans to the front side, the glasses loaded on the cassette 10 may slide down and fall off from the cassette 10 and may be broken. Therefore, the user should pay attention to prevent the leaning of the cassette 10 to the front side when carrying the cassette 10. In addition, since the conventional cassette supports only the edges of glasses with the protrusions 15' having short length, the central parts of the glasses is bent due to their weight. FIG. 4 shows the bent glasses 17 loaded on the conventional cassette 10, and the extent of bending of the glasses 17 having various sizes and thicknesses were measured and listed in the following table 1.
TABLE 1 Unit: mm SIZE OF THICKNESS OF EXTENT OF GLASS (mm.sup.2) GLASS BENDING 370 1.1 1.15 550 1.1 3.3 550 0.7 9.05
As shown in table 1, in case of the widely used liquid crystal display which is slim and of big size, the extent of bending is large, and it deteriorates the quality of the device.
In addition, the conventional cassette does not effectively eliminate the static electricity generated on the glasses when the glasses are loaded on the cassette. FIGS. 5A and 5B are the figures to show the parts of the glass where the electricity generated. FIG. 5A shows the front view of the glass and FIG. 5B shows the top view of the glass. The measured voltages due to static electricity according to the parts of the glass are shown in the following table 2. These values are measured 2 days after loading the glasses on the conventional cassette.
TABLE 2 UNIT: kV POSITION A, a B, b C, c EDGE OF GLASS 0.58 1.72 0.52 SURFACE OF GLASS 0.27 0.45 0.28
Even though the measured value of the static electricity may vary due to the conditions of measurements, it is clearly shown in table 2 that the static electricity generated on parts b and B in FIGS. 5A and 5B has higher values than those on the parts a, A and C, c of the glass. It means that the central part and the front side of the glass which may be easily in contact with the materials charged with electricity would have higher electricity. The static electricity is increased by the contact of the glass with a human body or other facilities. Table 3 shows that the variation of the static electricity of part B of FIG. 5B before and after the contact of the glass with the human body.
TABLE 3 UNIT: kV TIME 10 min 20 min 30 min BEFORE THE CONTACT 0.45 0.45 0.45 AFTER THE CONTACT 0.58 0.78 0.65
Generally, it is known that the static electricity generated on the glass and the slot of the cassette has the value between 200V and 2980V.